maintenance: recommended schedule in register/start

The 'git maintenance (register|start)' subcommands add the current
repository to the global Git config so maintenance will operate on that
repository. It does not specify what maintenance should occur or how
often.

If a user sets any 'maintenance.<task>.scheduled' config value, then
they have chosen a specific schedule for themselves and Git should
respect that.

However, in an effort to recommend a good schedule for repositories of
all sizes, set new config values for recommended tasks that are safe to
run in the background while users run foreground Git commands. These
commands are generally everything but the 'gc' task.

Author's Note: I feel we should do _something_ to recommend a good
schedule to users, but I'm not 100% set on this schedule. This is the
schedule we use in Scalar and VFS for Git for very large repositories
using the GVFS protocol. While the schedule works in that environment,
it is possible that "normal" Git repositories could benefit from
something more obvious (such as running 'gc' once a day). However, this
patch gives us a place to start a conversation on what we should
recommend. For my purposes, Scalar will set these config values so we
can always differ from core Git's recommendations.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>

Author: derrickstolee

Documentation/git-maintenance.txt

@@ -37,6 +37,12 @@ register::
 	`maintenance.<task>.schedule`. The tasks that are enabled are safe
 	for running in the background without disrupting foreground
 	processes.
++
+If your repository has no 'maintenance.<task>.schedule' configuration
+values set, then Git will set configuration values to some recommended
+settings. These settings disable foreground maintenance while performing
+maintenance tasks in the background that will not interrupt foreground Git
+operations.
 
 run::
 	Run one or more maintenance tasks. If one or more `--task` options

builtin/gc.c

@@ -1446,6 +1446,47 @@ static int task_option_parse(const struct option *opt,
 	return 0;
 }
 
+static int has_schedule_config(void)
+{
+	int i, found = 0;
+	struct strbuf config_name = STRBUF_INIT;
+	size_t prefix;
+
+	strbuf_addstr(&config_name, "maintenance.");
+	prefix = config_name.len;
+
+	for (i = 0; !found && i < TASK__COUNT; i++) {
+		int value;
+
+		strbuf_setlen(&config_name, prefix);
+		strbuf_addf(&config_name, "%s.schedule", tasks[i].name);
+
+		if (!git_config_get_int(config_name.buf, &value))
+			found = 1;
+	}
+
+	strbuf_release(&config_name);
+	return found;
+}
+
+static void set_recommended_schedule(void)
+{
+	git_config_set("maintenance.auto", "false");
+	git_config_set("maintenance.gc.enabled", "false");
+
+	git_config_set("maintenance.prefetch.enabled", "true");
+	git_config_set("maintenance.prefetch.schedule", "3500");
+
+	git_config_set("maintenance.commit-graph.enabled", "true");
+	git_config_set("maintenance.commit-graph.schedule", "3500");
+
+	git_config_set("maintenance.loose-objects.enabled", "true");
+	git_config_set("maintenance.loose-objects.schedule", "86000");
+
+	git_config_set("maintenance.incremental-repack.enabled", "true");
+	git_config_set("maintenance.incremental-repack.schedule", "86000");
+}
+
 static int maintenance_register(void)
 {
 	struct child_process config_set = CHILD_PROCESS_INIT;
@@ -1455,6 +1496,9 @@ static int maintenance_register(void)
 	if (!the_repository || !the_repository->gitdir)
 		return 0;
 
+	if (has_schedule_config())
+		set_recommended_schedule();
+
 	config_get.git_cmd = 1;
 	strvec_pushl(&config_get.args, "config", "--global", "--get", "maintenance.repo",
 		     the_repository->worktree ? the_repository->worktree

t/t7900-maintenance.sh

@@ -300,6 +300,11 @@ test_expect_success 'register and unregister' '
 	git config --global --add maintenance.repo /existing2 &&
 	git config --global --get-all maintenance.repo >before &&
 	git maintenance register &&
+	test_cmp_config false maintenance.auto &&
+	test_cmp_config false maintenance.gc.enabled &&
+	test_cmp_config true maintenance.prefetch.enabled &&
+	test_cmp_config 3500 maintenance.commit-graph.schedule &&
+	test_cmp_config 86000 maintenance.incremental-repack.schedule &&
 	git config --global --get-all maintenance.repo >actual &&
 	cp before after &&
 	pwd >>after &&